Introduction National practice guidelines recommend early aspirin administration to reduce mortality in acute coronary syndrome (ACS). Although timely administration of aspirin has been shown to reduce mortality in ACS by 23%, prior regional Emergency Medical Service (EMS) data have shown inadequate prehospital administration of aspirin in patients with suspected cardiac ischaemia.

Objectives Using the National EMS Information System (NEMSIS) database, we sought to determine (1) the proportion of patients with suspected cardiac ischaemia who received aspirin and (2) patient and prehospital characteristics that independently predicted administration of aspirin.

Methods Analysis of the 2011 NEMSIS database targeted patients aged ≥40 years with a paramedic primary impression of ‘chest pain’. To identify patients with chest pain of suspected cardiac aetiology, we included those for whom an ECG or cardiac monitoring had been performed. Trauma-related chest pain and basic life support transports were excluded. The primary outcome was presence of aspirin administration. Patient (age, sex, race/ethnicity and insurance status) and regional characteristics where the EMS transport occurred were also obtained. Multivariate logistic regression was used to assess the independent association of patient and regional factors with aspirin administration for suspected cardiac ischaemia.

Results Of the total 14 371 941 EMS incidents in the 2011 database, 198 231 patients met our inclusion criteria (1.3%). Of those, 45.4% received aspirin from the EMS provider. When compared with non-Hispanic white patients, several groups had greater odds of aspirin administration by EMS: non-Hispanic black patients (OR 1.49, 95% CI 1.44 to 1.55), non-Hispanic Asians (OR 1.62, 95% CI 1.21 to 2.18), Hispanics (OR 1.71, 95% CI 1.54 to 1.91) and other non-Hispanics (OR 1.27, 95% CI 1.07 to 1.51). Patients living in the Southern region of the USA (OR 0.59, 95% CI 0.57 to 0.62) and patients with governmental (federally administered such as Veteran's Health Care, but not Medicare or Medicaid) insurance (OR 0.67, 95% CI 0.57 to 0.78) had the lowest odds of receiving aspirin. Age and sex (OR 1.00, 95% CI 1.00 to 1.00) were not associated with aspirin administration.

Conclusions It is likely that prehospital aspirin administration for patients with suspected cardiac ischaemia remains low nationally and could be improved. Reasons for disparities among the various groups should be explored.